Observations are described in 12 massively (greater than 300 pounds) obese patients aged 25 to 59 years (mean 37) (5 women) weighing 312 to greater than 500 pounds (mean 381): 7 had had systemic hypertension; 4, hypersomnia or sleep apnea; 2, diabetes mellitus, and 1, symptomatic coronary artery disease. Five died suddenly from undetermined causes; 2, from right-sided congestive heart failure; 1, from acute myocardial infarction; 1, from aortic dissection; 1, from intracerebral hemorrhage; 1, from a drug overdose, and 1, post-operatively shortly after an ileal bypass. The heart weight was increased in all 12 patients. The heart weight to body weight ratio expressed as a percent ranged from 0.22 to 0.61 (mean 0.37) (normal for men = 0.42 to 0.46 [mean 0.43]; for women = 0.38 to 0.46 [mean 0.40]). The left ventricular cavity was dilated in 11 patients, and the right ventricular cavity, in 12. Only 2 patients (aged 42 and 59 years) had 1 or more major epicardial coronary arteries narrowed greater than 75% in cross-sectional area (XSA) by atherosclerotic plaque, 1 of whom had no symptoms of myocardial ischemia. Of 664 five-mm segments from the 4 major epicardial coronary arteries from 11 patients (mean 60 per patient), 431 (65%) were narrowed 0-25% in XSA; 143 (21%), 26-50%; 73 (11%), 51-75%, and 17 (3%), 76-100%. Thus, these extremely obese patients who died prematurely did not have more coronary atherosclerosis than might be expected for their ages.